The Eye

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What is the role of the conjunctiva?
It is a thin, transparent membrane that covers the cornea. It protects the cornea from damage.
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What is the role of the sclera?
It is a tough opaque tissue covering the eye. It protects the eye against damage. Is the site of attatchment of the eye musles.
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What is the ole of the aqueous humour?
It is a transparent watery fluid between the cornea and lens. It maintains the shape of the front of the eye.
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What is the role of the iris?
It is a muscular layer with circular ad radial muscle. It contains a pigment that absorbs light. It adjusts the size of the pupil to control the amount of light entering the eye.
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What is the role of the pupil?
It is the gap in the iris. The area through which light reaches the lens and enters the centre of the eye.
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What is the role of the ciliary body?
It contains the ciliary muscle. Suspensory ligaments extend from this and hold the lens in place. It adjusts the shape of the lens to focus light rays.
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What is the role of suspensory ligaments?
They connect the ciliary body to the lens. They transfer tension from the eyeball to make the lens thinner, this focuses the light rays of distant objects.
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What is the role of the lens?
It is a transparent biconcave structure with refractive properties. It refracts light and focuses light rays on the retina.
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What is the role of the Vitrous humour?
It a transparent, jelly-like material between the lens and the back of the eye. It maintains the shape of the rear of the eye and supports the lens.
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What is the role of the retina?
It is the inner layer of the eyeball containing light sensitive receptor cells. When stimulated, the rods and cones initiate impulses in associated neurones.
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What is the role of the fovea?
It is rich in cones and does not contain rods. Therefor it gives clearest daylight colour vision.
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What is the role of the choroid?
It is the layer of pigemented cells between the retina and sclera. It contains blood vessels that supply the retina. It prevents reflection of light back through the eye.
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What is the role of the optic nerve?
It is a bundle of sensory nerve fibres that leave the retina. It transmits impulses from the retina to the brain.
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What is the role of the blind spot?
It is the part of the retina where sensory neurones unite to form the optic nerve. This area contains no light sensitive cells so it is not sensitive to light.
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Where does refraction of light take place in the eye?
Most refraction of light takes place in the cornea. Further bending occures as light passes through the lens. By adjusting the lens' thickness, the light rays can be focused on the retina.
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How do you obtain a focused image of a distant object.
The light rays approaching the eye are parallel. The cornea refracts the light. Little additional refraction is needed to focus light on the retina. Therefore, The lens is thin, they ciliary muscles are relaxed & the suspensory ligaments are taught.
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How do you obtain a focused image of a close-up object?
Light rays diverge from a close-up object. Cornea refracts rays. Further refraction is needed to focus light on retina. => Thick lens -> Ciliary muscles are contracted and suspensory ligaments are slack.
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What is accomodation in terms of the eye?
The adjustment of lens thickness to ensure that the light rays are focused on the retina irrespective of the angle of the light rays reaching the eye.
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How does the eye control the amount of light entering the eye in low light?
Radial muscles contract. Circular muscles relax. The pupil is dilated, this lets in as much light as possible to ensure there is sufficient light to stimulate photo-receptors.
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How does the eye control the amount of light entering the eye in bright light?
Radial muscles relax. Circular muscles contract. The pupil is constricted, thsi restricts the amount of light enetering the eye as too much light may prevent the formation of an image or damage the light receptor cells.
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What does the retina contain?
Millions of light sensitive cells and the neurones with which the synapse.
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How are the rods and cones photoreceptors?
Light energy brings a change in the level of polarisation of their membranes. They act as transducers, converting a light stimulus to a nerve impulse in their associated neurones.
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What is the light sensitive pigment in rods?
Rhodopsin. It is packed into an array of membranes in the outer part of the cell.
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What is rhodopsin made from?
A protein called opsis and the light absorbing compound retinal.
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What happens when rhodopsin is stimulated by light?
Rhodopsin breaks down into opsin and retinal. This changes the membrane potential of the rod causing a generator potential. If threshold level is achieved the adjacent neurone will become depolarised and conduct an action potential.
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How is the rod adapted for low light intensities?
Rhodopsin will break down readily in low light levels, only requiring a small amount of light energy. In bright light virtually all the rhodopsin is broken down. It takes time to be re-synthesised.
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What is the pigment in cone cells called?
Iodopsin. It is situated in the membranes of the outer segment of the cell. It is less readily broken down so will only produce a generator potential in bright light.
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What determines colour vision?
Iodopsin exists in 3 diff forms. Each form is sensitive to different wave lengths of light (red, green & Blue). It is the degree of stimulation of each type of cone that determines colour vision.
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What is high visual acuity?
The ability of cones to provide highly precise colour vision of high resolution. This is because each cone cell can synapse individually with its own bipolar neurone.
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What is resolution?
The smallest measurable interval between two objects.
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What is lack of visual acuity?
Rods show retinal convergence as a number of rods have a common bipolar neurone. Retinal convergence allows individual rods to combine together and reach the threshold value to produce an action potential. It's also the basis of sensitivity of rods.
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What is summation?
Combination of multiple individual rods' generator potentials to cause an action potential in the bipolar neurone.
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What is binocular vision?
Presence of two eyes.
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What happens if the 2 eyes create a single image.
There is an accurate judgement of distance.
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What is the word for the ability to form 3-dimensional images?
Stereoscopic-vision.
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Why do predatory species have eyes on the front of their head?
It gives them excellent judgement of distance to prey and 3D vision.
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Why do prey species have eyes of the sides of their head?
To have a wider field of view. This is greater priority for prey species as it aids the detection of potential predators than having 3D vision.
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What is the role of the sclera?

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It is a tough opaque tissue covering the eye. It protects the eye against damage. Is the site of attatchment of the eye musles.

Card 3

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What is the ole of the aqueous humour?

Back

Preview of the front of card 3

Card 4

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What is the role of the iris?

Back

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Card 5

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What is the role of the pupil?

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